1. Field of the Invention
The present invention relates to a production method of a multilayer electronic device, such as a multilayer ceramic capacitor, and particularly relates to a production method of a multilayer electronic device, by which so-called a sheet attack phenomenon does not arise when forming an electrode pattern layer on a green sheet surface, consequently, a resultant electronic device has a low short-circuiting defective rate.
2. Description of the Related Art
As a method of producing a multilayer electronic device, such as a capacitor, piezoelectric element, PTC thermister, NTC thermister and varistor, for example, a method described below is known. Namely, ceramic slurry including a ceramic powder, organic binder, plasticizer and solvent, etc. is formed to be a sheet shape on a flexible supporting body (for example, a PET film) by the doctor blade method, etc. so as to obtain a green sheet first. A paste including an electrode material, such as palladium, silver and nickel, is printed in a predetermined pattern on the green sheet so as to obtain an electrode pattern layer.
When obtaining a multilayer structure, the obtained green sheets are stacked to obtain a desired multilayer structure and subjected to press cutting processing to be a ceramic green chip. A binder in the thus obtained ceramic green chip is burnt out, fired at 1000° C. to 1400° C., and a terminal electrode made by silver, silver-palladium, nickel or copper, etc. is formed on an obtained fired body, so that a ceramic multilayer electronic device is obtained.
When producing, for example, a multilayer ceramic capacitor by the above production method, a method of making a thickness of one dielectric layer thinner and increasing the number of stacked layers can be considered as a method of attaining a more compact body with a larger capacity. However, in the method of releasing a green sheet from a flexible supporting body and stacking, it is hard to release the green sheet from the flexible supporting body and the yield of stacking becomes very poor particularly in the case of a thin green sheet. Also, it is necessary to handle thin green sheets, characteristic defectives, such as short-circuiting, often occur in completed products.
As a method of solving such disadvantages, a method of obtaining a multilayer body by repeating a step of forming a green sheet and a step of printing an electrode on the green sheet (sheet coating and printing) exactly for the times of necessary number of layers to be stacked on a flexible supporting body may be considered. Due to this, releasing of the sheet from the supporting body becomes easier by an increased amount of the total thickness of the sheet (the patent article 1, etc. below).
However, this production method of the related art has problems as described below. The first disadvantageous point is that a step of printing an electrode pattern on a dried green sheet as a first layer is a Wet-on-Dry method. Namely, corrosion of a sheet portion of the first layer (sheet attack by a solvent) is caused by a solvent used when printing the electrode, so that a thickness of a sheet portion under an electrode printed portion becomes thin and short-circuiting easily occurs.
The second point is that when coating a sheet (wet-on Dry method) as a second layer (the case of the second layer is considered as an example), slurry to be coated as a second layer is soaked in the dried sheet portion of the first layer. As a result, disadvantages that sheet thicknesses become different between the first layer and the second layer, pinholes and other defective arise and the production characteristics are adversely affected.
The third point is that a step of printing an electrode after coating the second sheet and on (the case of the second layer is considered as an example) becomes a Wet-on-Dry method, so that a sheet portion of the second layer is corroded by a solvent used when printing the electrode. Therefore, a thickness of the sheet portion under the electrode printed portion becomes thin and short-circuiting is easily caused.
Particularly, when a sheet thickness of one layer is 3 μm or thinner and particularly when 1 μm or thinner, these disadvantages become notable and a compact multilayer ceramic capacitor having a large capacity becomes difficult.
[Patent Article 1] The Japanese Patent Publication No. 3190177